Phlegmonous Appearance in the Ipsilateral Paracardiac Fat without Paracardiac Lymph Node Enlargement on Chest CT Favors the Diagnosis of Pleural Tuberculosis over Malignant Pleural Effusion

This study investigated the potential role of paracardiac fat stranding (FS) interspersed with multiple fluid collections (FC) as a clue to differentiate between pleural tuberculosis (pleural TB) and malignant pleural effusion (MPE). The authors retrospectively analyzed chest computed tomography (CT) findings of 428 patients, 351 with pleural TB and 77 with MPE, focusing on the paracardiac fat, and level of pleural adenosine deaminase (ADA) and blood C-reactive protein (CRP). Two radiologists independently evaluated the chest CT findings regarding the paracardiac fat pad ipsilateral to the effusion, including FS, FC, phlegmonous appearance (a combination of the FS and multiple FC), and the presence of lymph node enlargement (>1 cm in short axis diameter). There were significant differences between patients with pleural TB and those with MPE with respect to the prevalence of phlegmonous appearance in the ipsilateral paracardiac fat (47.6% and 10.4%, p < 0.001, OR = 7.8; 95% CI 3.7–16.8) and paracardiac lymph node enlargement (1.4% and 19.5%, p < 0.001, OR = 0.06; 95% CI 0.02–0.2) on CT. In contrast, there was no difference in the prevalence of isolated FS or multiple FC within the ipsilateral paracardiac fat between the two groups. Median pleural ADA and serum CRP level were higher in patients with pleural TB accompanied by phlegmonous appearance in paracardiac fat compared to those without that appearance (ADA: median 104 IU/L versus 90 IU/L, p < 0.001; CRP: 6.5 mg/dL versus 4.2 mg/dL, p < 0.001). In conclusion, phlegmonous appearance in the ipsilateral paracardiac fat without paracardiac lymph node enlargement on chest CT favors a diagnosis of pleural TB over MPE.